1. Field of the Invention
The present invention relates to converting subsurface currents into electricity and, in particular, to conversion using a coil and magnetic element.
2. Description of Related Art
It is the experience of many who have gone to the seashore and stood in the water perhaps 10-50 yards from the water's edge that there is an extremely powerful alternating inflow and outflow of water 1-5 feet beneath the surface. This ebb and flow of water occurs about 4 times per minute and has tremendous kinetic energy.
In the past 50 years a number of different devices have been designed to try to harness the kinetic energy of moving ocean water in usable ways.
Tidal
Some energy conversion devices have relied on positioning at flood plains, such as those at the Bay of Fundy on the eastern coast of Canada or St. Malo on the Brittany Coast in France (across the La Rance Estuary). In these locations, there is a powerful inflow of water for a period of perhaps a few hours followed by a similar outflow of water for a similar period of time (“the tide comes in” and “the tide goes out”) each twice daily. Machinery at these locations requires huge capital investments, dam constructions, and other unsightly changes to the natural beauty of the sea.
Current
Some energy conversion devices have relied on positioning at the mouth of rivers or in the path of well-known ocean currents (really “current” generators erroneously called “tidal” generators) to supply a steady one-way directional source of moving water to turn turbines and other devices that then generate electricity.
These first two types of devices generally employ underwater propeller-like turbine wheels of various kinds to either generate electricity directly, or to mechanically transfer the turbine motion to a surface generator, or to run a pump to elevate water and thereby allow it to be used at some future time in a way similar to the generation of electricity at a hydroelectric dam.
Wave
Recently, instead of turbines, snake-like devices have been designed that feature multiple hinges (See New York Times Aug. 3, 2006, Pages C1 and C4) to allow the water to “whip” the device as it floats on the ocean's surface. These devices are not located to take advantage of subsurface back and forth motion of water, but rather are positioned as floating machinery miles off shore. They are surface wave devices. The motion at the joints of the device is harnessed to power small electric motors. Current designs of this device ride on the surface of the ocean where they are visible; not below the surface. These snake-like devices must be anchored to the ocean floor to work efficiently and to prevent them from drifting into land and being damaged. They are very confined mechanical devices that will eventually undergo fatigue and break.
Other wave energy conversion devices depend on buoys that contain magnets and float on the ocean surface within vertical cylindrical canisters that are in turn wrapped with copper wire. A linear electric generator is effectively created generating electricity by the action of fluctuating magnetic fields within the coil of copper wire. These are also wave machines that are positioned out to sea and do not take advantage of the subsurface back and forth motion of water. This method relies upon the “choppiness” of the surface water to operate efficiently; if the ocean is “calm”, only small amounts of electricity are generated.
Geothermal
Geothermal devices are used to harness the energy of underwater volcanoes and pipes driven deep into the ocean floor. These devices convert thermal energy and not mechanical energy into electricity.
Energy conversion patents include U.S. Pat. Nos. 1,439,984; 3,696,251; 4,291,234; 4,843,249; 4,864,152; 5,105,094; 5,440,176; 6,020,653; 6,729,744; 6,955,049; 7,012,340; and 7,042,112. See also www.aw-energy.com (unknown publication date) and “Permanent magnet fixation concepts for linear generator” by Oskar Danielsonn, et. al. Uppsala University, UPPSALA (unknown publication date).